1. Field of the Invention
The present invention relates to metallurgy and, particularly, to wear-resistant cast irons with high chromium content. Such cast irons can be used for manufacturing or reconditioning machine parts exposed to abrasive or abrasive and impact wear, for example, bucket teeth of rotary and other types of excavators, working members of hammer and jaw breakers, tools for drilling sedimentary rock, blades of bulldozers and scrapers. The above-mentioned parts or their working portions can be manufactured or reconditioned using the cast iron of the proposed composition mainly by electroslag remelting of ferrous electrodes in moulds the bottom and walls of which have the form corresponding to that of manufactured or reconditioned parts.
2. Description of the Prior Art
Wear-resistant cast irons with high chromium content are known in the art. Their wide use in present-day technology is determined, first, by their low cost as compared to that of diamond tools and tools made from hard alloys based on carbides of high melting metals such as tungsten, titanium and tantalum, second, by their sufficiently high impact strength, which quality is especially important in application involving impact loads and, third, by their adequate resistance to abrasive wear.
For example, an accepted Japanese Application No. 49-672 (Nat. class 12 B 151, 1974) describes a wear-resistant cast iron used for electric-arc surfacing of worn parts. This cast iron contains (wt.%) from 2.5 to 3.5 of carbon, from 0.5 to 2.0 of silicon, from 0.1 to 1.0 of manganese, from 5.0 to 20.0 of chromium, from 0.4 to 1.5 of boron, less than 1.0 of nickel, and the balance of iron and impurities.
Such cast iron is suitable for comparatively thin surface layers of parts abraded by contact with other metal or metal alloy parts, for example, for surfacing exhaust valve stem ends in internal combustion engines.
The use of such cast iron for manufacturing parts or components of machine parts exposed to impact and abrasive wear is impracticable due to an inadequate mechanical strength of said cast iron.
There is also known a higher-strength wear-resistant cast iron which can be used for manufacturing new or reconditioning used parts intended for service under impact and abrasive or abrasive wear conditions. This cast iron contains (wt.%) about 3.0 of carbon, about 1.0 of silicon, about 1.5 of manganese, up to 20.0 of chromium, about 0.5 of molibdenum, and the balance of iron and impurities (see Petrov I.V. "Primenenie iznosostoikikh naplavok dlya povysheniya dolgovechnosti rabochikh organov stroitelno-dorozhnykh mashin" in "Itogi Nauki" collected papers, "Svarka" Series, "Matallurgiya" Publishers, 1969).
However, parts made with the use of the above wear-resistant cast iron have a poor impact load resistance, this resulting in numerous cleavage fractures in surface layers and irregular distortions of the shape of said parts. The loss of specified shape by said parts causes higher both dynamic loads on machines concerned and specific energy consumption, this necessitating the replacement of said parts before they are actually worn out.
The most suitable for above application from among prior art ones is the Sormite I wear-resistant cast iron (see USSR State Standard GOST 21448-55) containing the following ingredients (wt.%):
______________________________________ carbon from 2.5 to 3.3 silicon from 2.8 to 3.5 manganese up to 1.5 chromium from 25 to 31 nickel from 3 to 5 iron and impurities the balance ______________________________________
When deposited in a thin layer on parts made from tough shock-resistant steels, this cast iron has good impact and abrasion resistance. However, due to a high silicon content and a coarse-grained microstructure, said cast iron exhibits a rather high brittleness in layers the thickness of which is comparable to or is larger than that of the steel portion of the part. Therefore, the use of such cast iron as a main structural material of working portions, for example, bucket teeth tips of rotary excavators, heads of breaker hammers and similar parts can result in a rapid failure of these working portions under impact loads.
A combined impact and abrasive action exerted on such parts having working portions from Sormite I reduces steel further the useful life thereof.